This invention relates to an electrically heatable thermostatic valve for a coolant circulation system of an internal-combustion engine, comprising a main valve which blocks a flow when the coolant is cold, a bypass valve which is open when the coolant is cold, and whose valve elements can be jointly adjusted with respect to stationary valve counterparts of a valve gear housing by a thermostatic working element that has a housing arranged in the valve gear housing, is situated in a coolant flow even when the main valve is closed and contains an expansion material and a working piston which is adjusted corresponding to the volume to the expansion material which is a function of the temperature.
Normally, thermostatic valves are constructed in such a manner that the valve element of the main valve and also the valve element of the bypass valve are mounted on the housing of the thermostatic working element. The working piston of the thermostatic working element is held in a stationary manner so that, in the case of a temperature-dependent volume change of the expansion material, the housing with the valve elements moves relative to the stationarily held working piston. In order to improve the controlling action of such a thermostatic valve, it is known from German Patent Document DE 30 18 682 A1 to arrange a heater plug with a heating resistance in the interior of the housing of the thermostatic working element and therefore inside the expansion material. The supplying of the heating resistance with electric energy takes place by means of lines which are guided through the stationary working piston.
It is also known, from German Patent Document DE 37 05 232 A1, to provide, instead of a thermostatic valve, a valve which can be controlled by a motor operator. In one embodiment, the motor operator is a thermostatic working element whose housing is stationarily arranged outside the valve gear housing. The working piston situated inside the valve gear housing is provided with a valve body which carries a main valve disk and a bypass valve disk in the arrangement known for thermostatic valves. The housing of the thermostatic working element serving as the motor operator extends transversely to a coolant pipe leading to the engine which is guided around the valve gear housing. The housing of the working element projects out of this pipe and is surrounded by a heating element in this area.
A control valve is known from U.S. Pat. No. 4,685,651 in which the working piston of a thermostatic working element is provided with a valve disk. In that arrangement, the housing of the thermostatic working element is stationarily arranged outside the area in which the medium flows which is to be controlled in the interior of the housing, a heating resistance is arranged which is supplied with electric energy via lines which are guided through the bottom of the housing of the working element that is opposite the working piston. In one embodiment, it is provided that the housing of the working element dips into another liquid flow so that the position of the working piston can also be determined by means of the temperature of this liquid.
It is an object of the invention to provide a thermostatic valve of the initially mentioned type which is distinguished by its increased operational reliability.
This object is achieved by the present invention in that the housing of the working element is held in a stationary manner by its end disposed opposite the working piston and is provided with an electric heating element, and in that the working piston is connected with the valve element of the main valve and the valve element of the bypass valve, in which case the valve element of the main valve forms in its closed position, together with the housing of the working element or its holding device, a sealing point blocking a flow, and is connected with the working piston via an open cage exposing the housing of the working element.
The invention is based on the recognition that a high operational reliability can be achieved only if the heating element and its supply lines are arranged in such a manner that, as a result, the sealing between the working piston and the housing of the thermostatic working element remains unaffected; that is, no lines must be guided through the working piston, nor is the working piston itself heated. It is therefore provided that the housing of the working element is arranged in a stationary manner so that then the heating element will be assigned directly to the housing and will be supplied by way of supply lines. As a result, it is possible to design the sealing between the working piston and the housing of the working element in a proven conventional manner without any impairment of its function by a heating element or supply lines. Because of the construction of the valve element of the main valve, the housing of the working element is always situated in the coolant flow which is cold at the start-up of the internal-combustion engine so that the thermostatic valve automatically opens up in a known manner when the coolant flow heats up and carries out the temperature control which is normal in the case of thermostatic valves. Because of the heating element, an additional controlled variable can be superimposed on this control.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.